Deceleration determination of a vehicle

ABSTRACT

A current state of a vehicle can be identified. At least a minimum acceleration capability of the vehicle is determined. A desired acceleration profile to follow is determined based at least in part on the minimum acceleration capability. An acceleration of the vehicle is controlled based at least in part on the desired acceleration profile.

BACKGROUND

Freeway and highway systems provide a network of controlled-access roadsthat deploy on-ramps and off-ramps for merging onto and egressing fromroadway. However, traffic congestion, especially on highways andfreeways, has become a bottleneck for commuters and travelers. Roadwaysuse has gone well above its intended vehicle capacity. Mechanisms aretherefore needed to facilitate driving on public roads to increasetraffic efficiency, reduce congestion, reduce risk of collisions, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary automated vehicle controlsystem.

FIG. 2 is an illustration of a freeway entrance ramp with a mergingvehicle.

FIG. 3 is an illustration of a vehicle making a left-turn across busytraffic.

FIG. 4 is an illustration of a vehicle making a left-turn across busytraffic and merging into a busy lane of traffic.

FIG. 5 is an illustration of a vehicle approaching other vehicles whichare blocking the autonomous vehicle's lane of traffic.

FIG. 6 illustrates an exemplary torque profile of a hybrid electricvehicle (HEV) for a five second interval.

FIG. 7 illustrates an exemplary velocity profile of the HEV of FIG. 6for the five second interval.

FIG. 8 illustrates an exemplary distance profile of the HEV of FIG. 6for the five second interval.

FIG. 9A is an illustration of an exemplary plot of three differentvehicles transient torque acceleration profiles.

FIG. 9B is an illustration of an exemplary plot of three differentvehicles transient velocity profiles.

FIG. 9C is an illustration of an exemplary plot of three differentvehicles transient distance profiles.

FIG. 10A is an exemplary illustration of an HEV acceleration responseover a time period.

FIG. 10B is an exemplary illustration of a naturally aspirated engine'sacceleration response over a time period.

FIG. 11 is an exemplary illustration of a plot of a naturally aspiratedengine with reduced capability due to one or more impeding factors.

FIG. 12 illustrates an exemplary maximum powertrain accelerationresponse of a powertrain.

FIG. 13A is an exemplary illustration of a predictive maximum braketorque capability response of a vehicle.

FIG. 13B is an exemplary illustration of a predictive maximum curvatureresponse of a vehicle.

FIG. 14 illustrates an exemplary discrete wheel torque plot of a hybridelectric vehicle (HEV) for a five second interval.

FIG. 15 illustrates an exemplary interpolated wheel torque plot of ahybrid electric vehicle (HEV) for a five second interval.

FIG. 16 is a flow chart illustrating an exemplary process of the systemfor calculating an acceleration profile.

FIG. 17 is a flow chart illustrating an exemplary process of the systemfor calculating a minimum acceleration capability profile.

FIG. 18 is a flow chart illustrating an exemplary process of the systemfor calculating a curvature performance profile.

DETAILED DESCRIPTION

Introduction

Merging onto a freeway, deaccelerating and egressing the freeway andmaking quick maneuvers around an obstacle represent difficult scenariosfor autonomous or non-autonomous vehicles. An illustration of anexemplary entrance ramp scenario is shown in FIG. 2, in which a vehicle32 is positioned on an entrance ramp 28 (merging lane) of a roadway 29.A vehicle 32 with a simplified powertrain model would typically chooseto slow down and possibly come to a complete stop and wait to merge intoa slot 33 behind a car 30. However, when the roadway 29 is highlycongested, a slot 33 accessible by a vehicle 32 using a conservativepowertrain model may not present itself in a timely manner. The vehicle32 system 10 disclosed herein provides knowledge of accelerationcapabilities of the vehicle 32 to facilitate merging into a slot that istimely available, such as slot 35 in front of a truck 31 and behind acar 39. In other words, a virtual driver, e.g., one or more computersexecuting programming to control some or all vehicle 32 operations, ofthe vehicle 32 can determine that the vehicle 32 has sufficientacceleration capability to safely merge the vehicle 32 into slot 35.

FIG. 3 shows another exemplary scenario in which the vehicle 32 isattempting to complete a left turn across busy traffic between the car30 and the car 39. FIG. 4 shows a similar left-turn across traffic, butin this case the vehicle 32 is also merging into traffic between car 30and car 39. FIG. 5 shows the vehicle 32 approaching the cars 30, 37, inwhich the path of the vehicle 32 is blocked. The vehicle 32 must eitherdecelerate before the cars 30, 37, and/or the vehicle 32 must maneuverabout the cars 30, 37. As with the exemplary scenario discussed aboveand shown in the figures, the virtual driver of the vehicle 32 can useknowledge of the vehicle longitudinal and lateral performance capabilityof the vehicle 32 in order to determine whether the vehicle 32 cansafely perform any desired maneuver.

Glossary

Certain words and terms used in this document will be recognized bythose skilled in the art and are intended to be accorded their plain andordinary meanings. Further, to facilitate explanation of the disclosedsubject matter, the following terms as used in this document havemeanings as set forth in the following paragraphs:

Profile—when herein used in the context of a physical quantity, e.g.,“torque profile,” refers to a set of values, e.g., that may be plottedon a graph, of the physical quantity, each of the values pertaining to amoment in time, e.g., having a time index.

Acceleration profile—is a rate of change of velocity of a vehicle over aperiod of time. For example, the acceleration capability profile can bea derived from a combination of the characteristics of the vehicle'sengine, transmission, hybrid motors and battery state of chargeoperating at their maximum capacity along with the vehicle mass andexternal factors like road grade.

Desired acceleration profile—is a plan of vehicle acceleration to beexecuted by an autonomous or semi-autonomous vehicle. It can bedetermined from a map stored in a computer memory, a desired route tofollow, a maximum acceleration capability of the vehicle, acommunication from another vehicle, a communication from an externalroad infrastructure system and an obstacle detection sensor.

Desired minimum acceleration profile—is a plan of vehicle decelerationto be executed by an autonomous or semi-autonomous vehicle. It can bedetermined from a map stored in a computer memory, a desired route tofollow, a minimum acceleration capability of the vehicle, acommunication from another vehicle, a communication from an externalroad infrastructure system and an obstacle detection sensor.

Desired curvature profile—is a plan of vehicle left and right maneuversto be executed by an autonomous or semi-autonomous vehicle. It can bedetermined from a map stored in a computer memory, a desired route tofollow, a maximum curvature capability of the vehicle, a communicationfrom another vehicle, a communication from an external roadinfrastructure system and an obstacle detection sensor.

Powertrain torque—the torque delivered to the wheels of the vehicle,i.e., the vehicle's total torque minus any torque to drive pumps forhydraulic systems and power any engine accessories.

Velocity profile—is the calculated velocity of the vehicle over a timeperiod and may be obtained by integrating the acceleration profile.

Distance profile—is the calculated distance for a time period and may beobtained by determining a second integral of the acceleration profile.

Torque profile—is a plot of torque over a fixed time period.

Acceleration rate limit—refers to a restriction or a vehicle'sacceleration capability.

Wheel torque limiting factors—limits to wheel torque and/or torquechanges. For example, torque is reduced to soften automatic transmissionshift changes when the transmission shifts gears. Another example of atorque limiting factor is a transmission torque limiter, which is adevice that protects the engine and drivetrain from damage by mechanicaloverload.

Maximum wheel torque—is the maximum torque available at the vehiclewheels. This torque value is the sum of all the factors that reducetorque at the wheels subtracted from the maximum torque the powertraincan produce. For example, factors that reduce torque can be anymechanical loss in the gears of the vehicle due to friction andchurning.

Transient torque—the changing values of torque as more or less power isapplied to a vehicle. For example, when the vehicle accelerates from astandstill with the maximum accelerator pedal, the torque increasesuntil the vehicle's engine power output is at its maximum and/or untilan equilibrium is obtained.

Steady state torque—occurs when the torque developed by the powertrainequals the desired torque within the limits of the system capability.

Motor torque limit value—is the maximum amount of torque a motor candeliver.

Torque balance distribution—is the values of the disseminated torque ateach wheel which can be adjusted to compensate for road and drivingconditions.

System power limit value—is the absolute system power determined by thewheel torque limiting factors, the engine power and a battery powerlimit (if a hybrid vehicle).

Gear churning—is the drag torque due to the rotation of discs submergedin a fluid, such as transmission gears in a transmission fluid.

Transient region—is the region of a plot where the acceleration ischanging quickly, e.g., prior and up to reaching a steady-state region.

Steady state region—is the region of a plot where the response ischanging slowly, limited by longer term physical capabilities of thepowertrain (e.g. battery power limits).

Max curvature—the minimum radius a vehicle can turn while maintainingthe lateral stability of a vehicle, which may take into accountpassenger comfort.

Road wheel angle—an angular measure of one or more wheels relative tothe longitudinal axis of the vehicle.

Path radius—the radius of an arc for the vehicle to navigate a path.

Left/Right capability—the vehicle's ability to execute and recover froma maneuver from one direction to another, for example, a lane change oran s-turn. The capability takes into account oversteer and understeer,road conditions, tire conditions and weather conditions, just to name afew.

Curvature—the turning radius of a vehicle.

Current curvature—the turning radius of a vehicle.

Steering system capability model—a model of the steering which caninclude an asymmetric left to right change value, a maximum rate ofchange of curvature and data from a suspension sensor.

Vehicle dynamic capability model—a model of the vehicle dynamiccapability which can include a ground reaction load at steer axle value,a bank, a surface mu, a CAN signal loss, a CAN signal corruption, apower supply level and a tire saturation.

Maximum rate of change of curvature—the maximum rate a vehicle canchange its curvature (turning radius) while maintaining the lateralstability of a vehicle, further possibly taking into account passengercomfort.

Asymmetric left to right change value—the asymmetric performance ofvehicle curvature when increasing the current direction bias versusdecreasing the current direction bias.

Capability of lateral movement—the vehicle's ability to maneuver toeither the right or to the left in a set time period at the vehicle'scurrent speed. For example, the vehicle's ability to change lanes whiletraveling at fifty-five mile per hour.

Basic system sizing—the mechanical characteristics of the vehicle. Forexample, the characteristics can include a vehicle mass (includingpassengers and cargo), a length, a width and a depth of the vehicle, andthe similar characteristics of any vehicles being towed.

Suspension geometry—specifies the structure and relationships ofsuspension components, for example the connection to knuckles and othersuspension components.

Understeer/oversteer gradient—is a coefficient of theundersteer/oversteer when the vehicle is executing a turn as a functionof a lateral acceleration value.

Ground reaction load at steer axle—road load affecting the steeringsystem statically or dynamically.

Road grade—a physical feature of the road that refers to the tangent ofthe angle of that road surface to the horizontal.

Bank—lateral as opposed to longitudinal inclination of the roadway,e.g., that either tilts the vehicle into or away from the center ofradius of curvature, typically measured in degrees.

Surface mu—coefficient of friction for the cumulative effects (snow,ice, water, loose material) and the texture of the road surface.

Split friction mu—is a road condition that occurs when the frictionsignificantly differs between the left and the right wheel path.

Componentry status—the collective status of the sensors, the controllersand systems within a vehicle.

Controller area network (CAN) signal loss—missing signals on the CANbus.

Controller area network (CAN) signal corruption—invalid signals on theCAN bus.

Power supply level—a present status of the voltage and current drawcapability at the controller connector derived from the any of thevehicle's power sources, i.e., the combination of the battery andalternator.

Tire saturation value—a point where a tire is unable to generateadditional lateral or longitudinal forces.

Vehicle mass—can include passengers, payload and towing.

Minimum acceleration capability—a change in velocity over time of avehicle in the decreasing direction.

Maximum acceleration capability—the maximum rate of change of velocityof a vehicle in the increasing direction.

Brake pad mu—scalar value which describes the ratio of the force offriction between the brakes and the rotor or drum when activated.Temperature, wear, water, oil and other factors can affect brake pad mu.

Vehicle pitch during dynamic braking—a longitudinal weight transfer whenbraking, i.e., loading of the front axle and unloading of the rear axle.

Load distribution—the distribution of the weight of the passengers,cargo, trailer tow weight and the vehicle itself that determinesindividual normal wheel forces.

Pressure distribution—the distribution of hydraulic brake fluid pressureat either an axle or an individual wheel.

Regenerative braking feedback value—a net effect of the regenerativebraking system on a vehicle braking performance. It is affected bygenerator sizing, battery state of charge, temperature, rate of minimumacceleration and other factors. These will affect what is the portion ofthe minimum acceleration that is captured regen energy or frictionalbrake heat. The blending of the two effects the overall stoppingperformance.

Active control feedback—a net effect of the driving assist systems whichhave an influence on stopping, e.g., ABS and stability control have adirect effect on an individual stop, but are also indications for moreconservative driving habits may be required.

Wheel speed sensors—sensors which can detect relative slip of tires bymeasuring individual wheel speeds.

Inertial sensor—a navigation aid that uses a computer, motion sensors(accelerometers) and rotation sensors (gyroscopes) to continuouslycalculate via dead reckoning the position, orientation, and velocity(direction and speed of movement) of a vehicle without the need forexternal references.

System Overview

In the Figures, like numerals indicate like elements throughout theseveral views. FIG. 1 shows an exemplary autonomous vehicle controlsystem 10. The system 10 can include a plurality of electronic controlunits (ECUs) communicatively coupled to a controller area network (CAN)bus 12, e.g., in a known arrangement. One such ECU coupled to the CANbus 12 is an autonomous vehicle controller (AVC) 14. The AVC 14 is asupervisory ECU that plans, coordinates and executes vehicle 32excursions and maneuvers. The AVC 14 is in communication with variousECUs which send data from various sensors and systems. For example, theAVC 14 can send and receive real time communications and data fromseveral of the vehicle 32 ECUs known collectively as an autonomousvehicle platform (AVP) 16. The AVP 16 can include a powertraincontroller 17, a steering controller 18 and a braking controller 20, abattery monitoring system ECU 22, a windows, doors, locks and mirrorscontroller 24, and a restraint controller 26. In addition, the AVC 14can request and receive real time environmental and road conditions viaa telematics controller 22.

The aforementioned controllers are also communicatively coupled to theCAN bus 12, e.g., in a known manner, in the example system 10. As isknown, a vehicle controller, such as for systems or controllersmentioned above, typically contains a processor and a memory, eachmemory storing instructions executable by the respective processor ofthe controller. Each controller memory may also store various data,e.g., data collected from other controllers or sensors in the vehicle32, such as may be available over the CAN bus 12, parameters foroperations of the controller, etc.

Autonomous Vehicle Controller

As the supervisory control controller, the AVC 14 provides overallcontrol of planning and operations of the autonomous vehicle 32. The AVC14 collects and evaluates pertinent data from the aforementionedcontrollers and sensors and monitors the status of the vehicle 32. Forexample, the AVC 14 can communicate with the ECUs to ascertain thecurrent state of the vehicle 32, including internal vehicle statesand/or environmental conditions. For example, the internal vehicle statecan include: a battery state of charge, a vehicle speed, an enginespeed, an engine temperature, a motor temperature, a batterytemperature, a list of failure modes, etc. The environmental conditionscan include, for example, an atmospheric pressure, an atmospherictemperature, a road grade, a road surface condition, etc.

Additionally, the AVC 14 can receive information from a GPS receiver, aset of road map data, a set of hybrid powertrain data, weather data anda forward determination sensor i.e., a LIDAR sensor, a SONAR sensor, anoptical range determination system, etc., e.g., via the CAN bus 12 inorder to make a path of travel determination. To determine a path oftravel, the AVC can include, for example, a set of possible futureroutes, a vehicle acceleration capability, a vehicle minimumacceleration capability, a vehicle lateral maneuvering capability, etc.

The AVC in typical driver assisted vehicles and self-driving, i.e.,autonomous vehicles, such as the vehicle 32 of FIG. 2, typically havesimplified models of the AVP system capability. This is in part due tolimitations in the amount of information we can transferred over the CANbus to the AVC 14. The AVC 14, and all of the other ECUs on the CAN bus12 may only be able to exchange a subset, i.e., less than all, of thedesirable AVP 16 information and/or other information available over theCAN bus 12 due to a volume of controller and ECU communications traffictraversing the CAN bus 12. As a result, the AVC 14 typically takes aconservative approach when planning a merge onto a highway, making turnsacross traffic or even leaving a highway, just to name a few possiblevehicle 32 maneuvers. This conservatism in path selection and controlcan result in the vehicle seeming sluggish and less refined. This couldbe prevented if the ECUs of the AVP 16 could provide timely, highfidelity vehicle capability information to assist the AVC 14 with itspath planning.

Autonomous Vehicle Platform

The ECUs of the AVP 16 have access to much more information about thevarious subsystems (powertrain, brakes, steering) of the AVP than couldbe made available over CAN bus 12 to the AVC 14. As a result, these ECUscan produce much higher fidelity models of their specific subsystemscapabilities in light of the current operating conditions, both internaland external. The AVP can then use these models to predict the truecapability of the vehicle 32, effectively condensing the multitude offactors down to profiles of system capability that is pertinent tolateral and longitudinal path planning control. For example, the AVP 16can determine the maximum available torque profile, which can be used tocalculate an associated acceleration capability profile of the vehicle32. In addition, the AVP 16 can provide a steering or curvatureperformance profile and a braking profile of the vehicle 32. Byproviding higher fidelity estimates of the system acceleration, minimumacceleration and steering capabilities from the AVP 16 to the AVC 14,the AVC 14 can be less conservative in its path planning and control ofthe vehicle 32.

Braking Controller

The braking controller 20 can monitor and control the vehicle 32 brakes,as well as any parameters affecting the stopping of the vehicle 32. Thebraking controller 20, for example, can assess and determine a minimumacceleration capability of the vehicle 32 by constantly requestingand/or receiving data related to minimum acceleration from variousvehicle 32 components and systems. The maximum brake torque capabilitycan be used to generate a braking profile, which can be sent to the AVC14 for determining how to decelerate the vehicle 32. The braking profilecan include the maximum brake torque capability along with a minimumacceleration capability.

Referring to FIG. 13A, an exemplary plot of a maximum brake torquecapability of a vehicle is shown. A maximum brake torque 98 is plottedover an exemplary time period t0 to t5. The time interval indexedbetween t0 to t1 represents a delay in the braking controller 20responding to a breaking request and no breaking torque is being appliedto the vehicle. The time from t1-t2 is the ramping up of the maximumbrake torque 98 from of the current braking torque value to a fullbreaking torque value and is based upon a maximum rate of possiblechange as determined by the braking controller 20. From time t2-t3 themaximum brake torque 98 is reduced, for example due to the pitchingmotion of the vehicle 32 as it is slowing. In the time frame t3-t4, themaximum brake torque 98 reduces even further due to brake fade. Brakefade is a term used to describe the partial or total loss of brakingpower used in a vehicle brake system. Brake fade occurs when the brakepad and the brake rotor no longer generate sufficient mutual friction tostop the vehicle at its preferred rate of deceleration.

The maximum brake torque capability is determined from such factors as abrake pad status, a hydraulic pressure status, a size of the vehicle 32,e.g., the vehicle 32 mass along with a vehicle payload and a towedobject mass, if any. Additional factors can include one or more of aroad grade value (slope), a road surface mu, a split friction mu, abrake pad mu, a pitch angle of the vehicle 32, a load distribution ofthe vehicle 32, a hydraulic brake pressure distribution of the hydraulicbrake fluid. Additionally, the braking controller can detect anabnormality on the brake pads and adjust the maximum brake torquecapability. For example, a groove in the brake pad or a liquid, e.g.,water or oil on the brake pad or even a contaminant on the brake pade.g., sand or dirt will affect the maximum brake torque capability.

The braking controller 20 can also monitor the vehicle 32 regenerativebraking interactions and evaluate how the regenerative braking affectsthe minimum acceleration of the vehicle 32. A regenerative brake, as isknown, is an energy recovery mechanism which decelerates a vehicle byconverting its kinetic energy into another form, such electrical energy,which can be either used immediately or stored until needed. Forexample, when the vehicle 32 is slowing, generators in the wheels can begenerating electricity and storing the energy in the vehicle 32 batterywithout the brake pads coming into contact with the wheels.

The braking controller 20 can also monitor the vehicle 32 activecontroller status. For example, an anti-lock braking system (ABS)status. ABS is a vehicle safety system that allows the wheels tomaintain tractive contact with the road surface according to driverinputs while braking, preventing the wheels from locking up (ceasingrotation) and avoiding uncontrolled skidding. Another example of anactive control function is traction control. Traction control is avehicle system which reduces power to a wheel when torque is mismatchedto road surface conditions, e.g., when the wheels slipping.

Additionally, the braking controller 20 can monitor a componentry statusof the braking system for problems with any its components. For example,the braking controller 20 can determine how a defective hydraulicproportioning valve component is going to affect the maximum braketorque capability of the vehicle 32 and then send a message to the AVC14, alerting the vehicle of a possible diminished stopping capability.

The braking controller 20 can use a vehicle sensor, for example, a wheelspeed sensor (not shown) and an accelerometer (not shown) with forwardlooking information to assist the AVC 14 with planning a deceleration.The forward looking information can be obtained from a map stored in thememory and can include, for example, road grade, elevation changes, roadbank information collected information from previous excursions, just toname a few. In addition, the vehicle 32 can obtain forward lookinginformation via a download from a vehicle-to-infrastructure (V2I)database (not shown) via the vehicle 32 telematics unit 23. The forwardlooking information can also be downloaded from a vehicle-to-vehicle(V2V) exchange.

Steering Controller

The steering controller 18 can monitor and control the steering systemof the vehicle 32. The steering controller 18 can generate a maximumcurvature profile which can be sent to the AVC 14 for use whendetermining steering maneuvers. For example, the maximum curvatureprofile can be produced from such elements as a lateral acceleration ofthe vehicle 32, a road wheel angle, a steering wheel angle, a yaw rate,a path radius, a right and a left (lateral) maneuver capability, amaximum rate of change of curvature the vehicle can execute and alateral asymmetry. The lateral asymmetry is an asymmetric difference inthe vehicle's ability to perform a left maneuver as opposed to a rightmaneuver. Additionally, the maximum curvature profile can also comprise,for example, a size of the vehicle 32, a ground reaction load at thesteering axle, a bank angle, a road surface coefficient value and asuspension geometry, etc.

The steering controller 18 can also monitor the steering system forproblems with any its components. Once the steering controller 18determines that a component may be faulty and is not performing asexpected, the steering controller further determines how the turningcapabilities of the vehicle 32 are diminished. The steering controller18 can then send a message to the AVC 14 alerting the vehicle of adiminished turning capability.

The steering controller 18 working with the AVC 14 can also use thevehicle sensors, for example, the wheel speed sensors, the accelerometerand the inertial sensor with forward-looking information to determine ifthe maximum curvature profile of the vehicle 32 will be appropriate forthe upcoming road conditions. For example, an accident in the roadrequires that the vehicle 32 equipped with a trailer make a turn with aten meter radius turn to get around the accident. The maximum curvatureprofile indicates the vehicle with the trailer may only be able tomanage a 12 meter turn radius, in which case the AVC 14 would have todetermine an alternative route. The forward-looking information can beobtained from a map stored in the memory and can include, for example,road grade, elevation changes, road bank information collectedinformation from previous excursions, just to name a few. In addition,the vehicle 32 can obtain forward looking information via a downloadfrom a vehicle-to-infrastructure (V2I) database (not shown) via thevehicle 32 telematics unit 23. In addition, the forward-lookinginformation can also be downloaded from a vehicle-to-vehiclecommunications system, e.g., from another vehicle.

Powertrain Controller

The powertrain controller 17 can monitor and control the powertrainsystem of the vehicle 32. It can calculate torque values based on highfidelity static and dynamic models of the powertrain system using datareceived at the sensors and the internal states of the system. Forexample, the powertrain controller 17 can monitor the high voltagebattery and high voltage battery system of the vehicle 32 to determinehow much of the high voltage battery capacity is available to assistwith torque generation at the vehicle's motors. Additionally, thepowertrain controller 17 can monitor and regulate the combustion enginetorque contribution accounting for the effect of internal factors(failure modes, engine temperature, rate of change and range ofactuators like throttle, variable cam, etc.) and external factors(altitude, atmospheric temperature, humidity, etc.). These torquecapability estimates can then be converted to an equivalent accelerationcapability estimates using vehicle mass, road grade, tire radius, andthe road surface coefficient of friction.

Other Systems

The battery monitoring system ECU 22 is responsible for monitoring andmaintaining the high voltage (HV) battery of the autonomous vehicle 32.The battery monitoring system ECU 22 sends information regarding thestate of charge of the hybrid HV battery system. The windows, doors,locks and mirrors ECU 24 monitors and controls the windows, doors, locksand mirrors of the autonomous vehicle 32. The restraint controller ECUis responsible for the vehicle 32 safety equipment, such as air bags,seat belt tensioners and any other passenger protection systems.

Modeling Maximum Acceleration Capability as Distance and Speed Profiles

To safely make a merge or a turn, some considerations involved in thecalculus can include a distance to be traversed as well as any changesin velocity that would be required to execute the maneuver. Referringback to FIG. 2, the vehicle 32, e.g., the AVC 14, will need to determinethat the vehicle 32 can safely traverse a required distance in anappropriate time to get into the slot 35 or alternatively, merge intothe slot 33 taking into account the speed of the traffic flow on theroadway 29. When both conditions can be determined and met, the vehicle32 can then proceed and accelerate to merge into the slot 33. In otherwords, the vehicle 32 will have to conclude that the vehicle 32 is fastenough and can generate enough torque to safely maneuver into the slot35, or alternatively, slot 33.

A velocity profile and a distance profile of the vehicle 32 can bedetermined if an acceleration profile of the vehicle 32 is available,i.e., by integrating the acceleration profile to produce the velocityprofile and subsequently integrating the velocity profile to create thedistance profile.

FIG. 6 illustrates an exemplary wheel torque profile of a hybridelectric vehicle 32 over five seconds, where at time zero the vehicle 32is stopped and may be idling. Given the road grade, vehicle mass and awheel radius, one can generate an equivalent acceleration profile. FIGS.7 and 8 show the corresponding velocity profile and distance profilesderived from the wheel torque profile of FIG. 6. For instance, if theAVC 14 obtains the torque profile for a five second interval, the AVC 14can ascertain the corresponding velocity profile of the vehicle 32 overthe five seconds. The AVC 14 can typically also ascertain the vehicle 32distances within the same five seconds. For example, with reference toFIGS. 6-8, at a time index of one second, the maximum wheel torque(vertical axis) being delivered to the powertrain is approximately 1200Newton-meters. The velocity produced in the transient region at onesecond (horizontal axis) would be approximately 19.8 meters per second(vertical axis) and the distance traveled would be approximately 19meters (vertical axis). At time equals four seconds, the steady statetorque would be approximately 230 Newton-meters, the velocity would beapproximately 25.3 meters per second, and the distance traveled would beapproximately 86 meters.

The plots of FIGS. 9A, 9B, and 9C illustrate profiles of three transientaccelerations of three different vehicles (or the same vehicle underdifferent conditions). A first vehicle 81 has a first order filterresponse for acceleration. A second vehicle 82 starts with a straightline acceleration which then flattens out. A third vehicle 83 beginswith a rapid acceleration increase which then flattens out and thenincreases again. All three acceleration profiles have the same finalsteady state acceleration at a time index of five seconds. However, asillustrated in FIGS. 9B and 9C, the resulting velocities and distancestraveled, respectively, over the five seconds are significantlydifferent. Therefore, as each vehicle's acceleration profile differs,the calculation of the each particular vehicle's velocities anddistances are also differ which could significantly impact the mostappropriate path to select for an autonomous vehicle. Therefore, usingreal time vehicle performance capability data is crucial for pathplanning of the vehicle 32 and must be taken into account whendetermining the vehicle's merging capabilities.

Typical Maximum Vehicle Acceleration Response

A typical maximum pedal response and the corresponding accelerationprofile varies depending on the type of engines, motors and thepowertrain, e.g., the performance characteristics of a battery electricvehicle (BEV) are different than those of a hybrid electric vehicle(HEV) or even of a gas or a gas turbo vehicle. For example, whendetermining the maximum capability of the system, the AVP can take intoconsideration a current gear ratio between the engine/motor and thewheels, a driver selectable mode, a vehicle calibration, any drivabilityfilters, an engine On/Off state, gear ratios between the engine/motorand the wheels, etc. Common performance considerations for a hybridvehicle and other vehicles when considering the maximum propulsivecapability characteristics include whether the vehicle is moving or at astandstill, the size of the engine, the current transmission gear andcalibrations, just to name a few.

FIG. 10A is an illustration of an exemplary acceleration plot 90 of theresponse of a hybrid electric vehicle. The time interval from t0 to t1of the plot 90 represents a delay due to the time it takes for thesystem to recognize a change in a torque request (e.g., from input to anacceleration pedal) and initiating a response from the actuators. Theinitial rise from t1 to t2 reflects the fast torque response providedvia the electric motor. The time from t2 to t3 represents a decrease inacceleration (slope) as the HEV engages the combustion engine. Duringthe time from t3 to t4, the acceleration rate increases again as thecombustion engine contributes to the overall wheel torque and thevehicle's acceleration.

FIG. 10B is an illustration of an exemplary acceleration plot 91 of theresponse of a naturally aspirated combustion engine. As in the case ofthe HEV discussed above, the time delay from indexes t0 to t1 of anaspirated plot is due to the request and the initiation of the responsefrom the actuators. As compared to the HEV example in FIG. 10A, theinitial delay will likely be longer due to the gasoline engine'sactuators, as they are characteristically sluggish to respond comparedto the electric motor in a HEV. In the time period from indexes t1 tot4, the acceleration rate increases similarly to that of a first orderfilter as the manifold fills with air and the engine cylinders ingestmore air, which allows the engine to create more torque and vehicleacceleration.

The acceleration capability for the naturally aspirated engine may beimpeded at times by various factors: for example; an engine temperature,a barometric pressure, a fuel volatility rating, a fuel octane rating, afuel additive, a humidity level, a combustion chamber deposit value, analtitude value, an engine age, faults within certain components, etc. Anengine torque performance profile can then be sent to the AVC 14 for usein determining the vehicle 10 acceleration. FIG. 11 is an exemplaryillustration of plots of a naturally aspirated engine. Plot 93illustrates a reduced acceleration capability of an exemplary vehicledue to one or more of the above mentioned impeding factors, while plot93 illustrates an unimpeded acceleration capability of the exemplaryvehicle.

Predicting the Acceleration Profile

To obtain an accurate powertrain model of the vehicle, the AVC 14, canuse the maximum curvature profile, the maximum brake torque capabilityand the acceleration profile from the from the vehicle control systemsECUs, i.e., the steering controller 18, the powertrain controller 17,and the braking controller 20. For example, the powertrain controller 17can calculate the maximum wheel torque acceleration response and send itto the AVC 14. FIG. 12 illustrates a simulated calculated exemplarymaximum wheel torque acceleration response 95. A transient torqueprofile is generated for a transient region 96 of the maximum wheeltorque acceleration response 95. In this region 96, the acceleration isincreasing. A steady-state torque profile can also be determined for asteady-state region 97 where the maximum wheel torque accelerationresponse 95 begins to decline because of the physical capabilities ofthe powertrain, such as the wheel torque limiting factors.

The maximum wheel torque acceleration response 95, which is thecombination of the transient torque profile and the steady-state torqueprofile, can be used to generate a max torque profile for a givenenvironment. This torque profile can be converted into an equivalentacceleration profile by accounting for things like vehicle mass, roadgrade, tire size, etc. As discussed above, the capability profile can besent to the AVC 14 to aid in selecting the best a planning profile (i.e.path to follow). However, sending the entire profile to the AVC 14 overthe CAN bus 12 may not be feasible due to CAN bus 12 bandwidth and timelimitations. Therefore, the transmitted profiles can be sampled at afinite number of discrete values at fixed time steps. For example, FIG.14 illustrates a sampled or discrete point wheel torque, whichidentifies the wheel torque capability of the vehicle 32 at respectivediscrete times. The finite number of points of the sampled wheel torqueprofile are then sent over the CAN bus 12 to the AVC 14. The AVC 14 theninterpolates the finite number of points to produce an interpolatedwheel torque profile, as shown in FIG. 15. For example, the AVC 14, canusing the interpolated wheel torque profile to determine the vehicle 32planning profile. Knowing how the vehicle 32 will operate over a timeperiod, which is five seconds in this example, allows the AVC 14 toactuate various vehicle 32 components, such as throttle or acceleratorpedal, steering, etc., according to a determined planning profile and acurrent driving situation, e.g., a requirement to merge, change lanes,etc. That is, the planning profile has an acceleration capability, i.e.,a maximum available acceleration, over the time axis of the planningprofile. Based on available acceleration indicated by the planningprofile, the AVC 14 may make decisions concerning propulsion and/orsteering control to achieve a merge and/or lane change maneuver, e.g.,by determining that the vehicle 32 can accelerate to achieve a slot 35,etc.

Referring to FIG. 5, the vehicle 32 is approaching an obstaclecomprising the vehicle 30 and the vehicle 37, which for example, mayhave been involved in an accident. The vehicle 32 must plan anappropriate action before the obstacle. For example, the vehicle 32 candeaccelerate and stop before the obstacle, the vehicle can deaccelerateand maneuver around the obstacle or the vehicle 32 can simply maneuveraround the obstacle. The vehicle 32 can use a minimum decelerationcapability along with the maximum curvature capability to plan anappropriate maneuver to traverse the obstacle.

Maximum Curvature Capability

FIG. 13B is an exemplary illustration of example of a future maximumcurvature capability signal (FMXCS) 99 exchanged between the steeringcontroller 18 and the AVC 14. A maximum left/right curvature capabilityis the vertical axis which is plotted against time in the horizontalaxis. The time interval from indexes t0 to t1 represents a delay in thesteering controller 18 responding to the AVC 14 request for the maximumleft/right curvature capability from and the therefore, the FMXCS 99 hasnot been determined. The time from t1-t2 is the ramping up from acurrent curvature rate to a full curvature rate of the FMXCS 99 basedupon a maximum rate of possible change as determined by the steeringcontroller 18. From time t2-t3 the FMXCS 99 rate is reduced. Forexample, the maximum curvature rate is reduced when the system 10detects an understeer or oversteer condition of the vehicle 32. In thetime frame t3-t4, the FMXCS 99 is reduced even further. For example,when system 10 detects the vehicle 32 is rolling.

Process Flow

FIG. 16 is a flow chart illustrating an exemplary process 100 of thesystem 10 for calculating the wheel torque profile of the vehicle 32from which the acceleration profile can be generated if we know the roadgrade, vehicle mass, and tire radius.

The process 100 begins in a block 110, in which a system status isobtained by the AVC 14. The AVC 14 determines the system status fromdata the AVC 14 receives from the various ECUs on the CAN bus 12. Thesystem status can include one or more quantities related to vehicle 32operation, e.g., a current vehicle speed, a current battery state ofcharge, a current wheel torque value, a transient torque value, a steadystate torque value, a wheel torque over time (see, e.g., FIG. 11),temperature and/or other similar information related to determining anacceleration profile. In addition, the AVC 14 can monitor a CAN Busstatus, a power supply level, and a tire saturation value, which can beincluded in the vehicle 32 system status.

Next, in a block 120, the powertrain controller 17 computes a transientwheel torque for the transient region 96 of the plot of wheel torque(e.g., FIG. 11). The transient wheel torque can be limited by factorswhich can reduce the total torque available to the vehicle and thereforenegatively affect the acceleration of the vehicle. The wheel torquelimiting factors can be intentionally implemented using known mechanicalor electronic techniques. For example, torque is often reduced to softenthe shifting of a transmission. Another example of a torque limitingfactor is a transmission input torque limit protects the transmissionand drivetrain from damage by a mechanical overload.

Next, in a block 130, the process 100 determines the wheel torquelimiting factors for the steady-state region 97. The wheel torquelimiting factors for the steady state region 97 can include an enginetorque limit, the motor torque limit and the battery system power limit.The engine and motor torque limits are the maximum amount of torque theengine and motor, respectively, can deliver. The system power limit isthe maximum available battery power available to the motors of theautonomous vehicle 32.

Next, in a block 140, the system 100 determines a predicted maximumwheel torque profile. The maximum wheel torque is the maximum torqueavailable at the wheels from all propulsion devices (e.g. a typicalpower split hybrid vehicle will have contributions from an engine andmotor) minus any mechanical losses. For example, the mechanical lossescan be due to a transmission gear friction or due to gear churning. Gearchurning is the drag torque due to the rotation of discs submerged in afluid, such as transmission gears in a transmission fluid.

Next, profile in a block 150, the predicted maximum acceleration profileis computed. Factors for computing the predicted maximum accelerationprofile from the predicted maximum wheel torque profile from block 140,can include the total mass of the autonomous vehicle 32 includingpassengers and luggage, the road grade, the radius of the wheels, brakecontrol interventions and the road surface conditions. The brake controlinterventions can include the electronic stability control, rollstability control and traction control. Road factors can include thedynamic interaction between the vehicle's tire and the road surface andnegative road surface conditions, such as rain or ice createinefficiencies of the autonomous vehicle 32 use of torque forpropulsion, as energy is lost by spinning or slipping tires.

Next, in a block 160, some or all of the maximum acceleration profiledetermined in the block 150 is provided to the AVC 14, which can use thepredicted maximum acceleration profile to determine the most appropriatepath given the current conditions, capability of the AVP 16 and desiredbehavior.

The predicted set of torque values and/or the maximum accelerationprofile could, in theory, or given an environment with the rightprocessing and network capacity, can be transferred from the powertraincontroller 17 to the AVC 14. However, as discussed above, sending anentire profiles to the AVC 14 over CAN bus 12 is generally not feasibledue to CAN bus 12 bandwidth limitations. Therefore, a finite number ofdiscrete points can be extracted from the profile at fixed time steps,e.g., as illustrated in FIG. 14. The finite number of points in thesampled maximum acceleration capability values are then sent over theCAN bus 12 to the AVC 14.

Using the sampled acceleration profile, the AVC 14 interpolates thefinite number of points to produce an interpolated planning maximumacceleration profile, as shown in FIG. 15. The interpolated planningmaximum acceleration profile is then used by the AVC 14, along with thecurrent situational awareness (an understanding of the relativepositions and velocities of the vehicles in the surrounding area) toplan and select the most appropriate path given the current conditions,reported capability of the AVP and desired behavior. The selection ofthe most appropriate path will be aided by limiting the number of pathsto evaluate and select from, to only those that can be robustly achievedby the autonomous vehicle 32 via acceleration requests to the AVP 16.During a merge and/or lane change maneuver the AVC 14 can rule out anypaths that are unachievable by the autonomous vehicle under currentconditions. Following the block 160, the process 100 ends.

Following the block 160, the process 100 ends.

FIG. 17 is a flow chart illustrating an exemplary process of the system10 for calculating the braking profile of the vehicle 32.

The process 200 begins in a block 210, in which a system status isobtained by the AVC 14. The current vehicle 32 state can include thevarious items as described in the block 110 of the process 100.

Next, in a block 220, the braking controller 20 retrieves parametersrelated to a stopping capability from memory or from other ECUs,including, e.g., a size of the vehicle 32, which is the vehicle 32 massalong with any additional payload and can include any objects thevehicle 32 may be towing. Additional factors include a road grade value(slope); a road surface mu, a brake pad mu, a pitch angle of the vehicle32, a load distribution of the vehicle 32, a pressure distribution ofthe hydraulic brake fluid and detection of any wear or contaminants onthe brake pads, such as grooves, water and oil.

Next in a block 230, the braking controller 20 retrieves data from thevehicle 32 regenerative braking system. For example, whether the vehicle32 is slowing and generating electricity and how much stopping torquethe wheel motors can contribute to the stopping ability of the vehicle32.

Next in a block 240, the braking controller 20 receives data from one ormore vehicle 32 stopping systems. For example, the braking controller 20may detect a brake system fault, for example, an optical sensor on oneof the wheel rotors is faulty or a hydraulic fluid level sensor mayindicate that the hydraulic fluid level is low and there may be apotential issue with the stopping distance.

Next in a block 250, the braking controller 20 determines from the abovefactors a braking profile.

Next in a block 260, the braking profile is sent to the ACV 14 for usein determining how maneuvers the vehicle 32 will be executed. Forexample, with reference to FIG. 5, the AVC 14 detects that the vehicle32 path is blocked by the car 30 and the car 37 and that there may notbe a safe path to travel around the cars. The AVC 14 can then use thebraking profile to determine how to effectuate a safe minimumacceleration before the cars 30 37. The AVC 14 can send the brakingcontroller 20 appropriate commands to actuate and monitor the brakingsystem. Additionally, the AVC 14 can send commands to the powertraincontroller 17 to reduce or turn off the any energy being applied to thevehicle 32 propulsion system.

Following the block 260, the process 200 ends.

FIG. 18 is a flow chart illustrating an exemplary process of the system10 for calculating the maximum curvature profile of the autonomousvehicle 32.

The process 300 begins in a block 310, in which a system status isobtained by the AVC 14. The current vehicle 32 state can include thevarious items as described in the block 110 of the process 100.

Next, in a block 320, the steering controller 18 retrieves from memory aset of physical characteristics of the vehicle 32. For example, thephysical dimensions of the vehicle, weight of the vehicle 32, a minimumturning radius, a center of gravity of the vehicle 32, and anundersteer/oversteer gradient value, etc.

Next in a block 330, the steering controller 18 retrieves data from thevehicle 32 steering system's sensors. For example, the received data mayinclude the ground reaction load at the steering axle, the bank angle ofthe vehicle and trailer, a road surface coefficient value, and vehicle32 suspension status.

Next in a block 340, the steering controller retrieves forward lookingdata to assist in the determination of the maximum curvature profile.For example, the steering controller 18 can use the wheel speed sensorsand the accelerometer with forward looking information to furtherdetermine the maximum curvature capability of the vehicle 32 at a givenspeed. For example, the vehicle 32 can be traveling at 100 kilometersper hour. If the vehicle 32 was required to make a turn to avoid anobstacle, the radius of the turn would be larger than if the vehicle wasto safely make the same maneuver at 30 kilometers per hour. The forwardinformation can be obtained from the map stored in the memory of thesteering controller 18. The map can include, for example, road grade,elevation changes, road bank information collected information fromprevious excursions, just to name a few. As discussed above, the vehicle32 can obtain forward-looking information via a download from avehicle-to-infrastructure (VTI) database (not shown) via the vehicle 32telematics unit (not shown). The forward-looking information canadditionally or alternatively be downloaded from a vehicle-to-vehicledata transfer.

Next in a block 350, the steering controller 20 determines whether thereare any component problems with the steering system. For example, awheel speed sensor may be sporadically reporting the wheel speed. Anerroneous wheel speed would have an effect on how the steeringcontroller would determine the surface traction coefficient, which inturn can affect how the vehicle 32 would execute a turn or evasivemaneuver.

Next in a block 360, the braking controller 20 determines from the abovefactors the maximum curvature profile.

Next in a block 370, the maximum curvature profile is sent to the ACV 14for us in determining any maneuvers the vehicle 32 may have to make. Forexample, with reference to FIG. 5, the AVC 14 detects that the vehicle32 path is blocked by the car 30 and the car 37 and that there is a safepath to travel around the cars 30 37. The AVC 14 can then use themaximum curvature profile to determine how to effectuate a safe maneuveraround the cars 30 37. The AVC 14 can send the steering controller 20appropriate commands to actuate steering system to effectively maneuverthe vehicle 32 around the cars 30 37. Additionally, the AVC 14 may sendcommands to the powertrain controller 17 and the braking controller 20to slow the vehicle 32 while maneuvering to avoid the cars 30, 37.

Following the block 370, the process 300200 ends.

Conclusion

As used herein, the adverb “substantially” modifying an adjective meansthat a shape, structure, measurement, value, calculation, etc. maydeviate from an exact described geometry, distance, measurement, value,calculation, etc., because of imperfections in the materials, machining,manufacturing, sensor measurements, computations, processing time,communications time, etc.

Computing devices such as those discussed herein generally each includeinstructions executable by one or more computing devices such as thoseidentified above, and for carrying out blocks or steps of processesdescribed above. Computer executable instructions may be compiled orinterpreted from computer programs created using a variety ofprogramming languages and/or technologies, including, withoutlimitation, and either alone or in combination, Java™, C, C++, C#,Visual Basic, Java Script, Perl, HTML, PHP, etc. In general, a processor(e.g., a microprocessor) receives instructions, e.g., from a memory, acomputer readable medium, etc., and executes these instructions, therebyperforming one or more processes, including one or more of the processesdescribed herein. Such instructions and other data may be stored andtransmitted using a variety of computer readable media. A file in acomputing device is generally a collection of data stored on a computerreadable medium, such as a storage medium, a random access memory, etc.

A computer readable medium includes any medium that participates inproviding data (e.g., instructions), which may be read by a computer.Such a medium may take many forms, including, but not limited to,non-volatile media, volatile media, etc. Non-volatile media include, forexample, optical or magnetic disks and other persistent memory. Volatilemedia include dynamic random access memory (DRAM), which typicallyconstitutes a main memory. Common forms of computer readable mediainclude, for example, a floppy disk, a flexible disk, hard disk,magnetic tape, any other magnetic medium, a CD ROM, DVD, any otheroptical medium, punch cards, paper tape, any other physical medium withpatterns of holes, a RAM, a PROM, an EPROM, a FLASH EEPROM, any othermemory chip or cartridge, or any other medium from which a computer canread.

With regard to the media, processes, systems, methods, etc. describedherein, it should be understood that, although the steps of suchprocesses, etc. have been described as occurring according to a certainordered sequence, such processes could be practiced with the describedsteps performed in an order other than the order described herein. Itfurther should be understood that certain steps could be performedsimultaneously, that other steps could be added, or that certain stepsdescribed herein could be omitted. In other words, the descriptions ofsystems and/or processes herein are provided for the purpose ofillustrating certain embodiments, and should in no way be construed soas to limit the disclosed subject matter.

Accordingly, it is to be understood that the above description isintended to be illustrative and not restrictive. Many embodiments andapplications other than the examples provided would be apparent to thoseof skill in the art upon reading the above description. The scope of theinvention should be determined, not with reference to the abovedescription, but should instead be determined with reference to claimsappended hereto and/or included in a non-provisional patent applicationbased hereon, along with the full scope of equivalents to which suchclaims are entitled. It is anticipated and intended that futuredevelopments will occur in the arts discussed herein, and that thedisclosed systems and methods will be incorporated into such futureembodiments. In sum, it should be understood that the disclosed subjectmatter is capable of modification and variation.

What is claimed is:
 1. A system, comprising a computer having aprocessor and a memory, the memory storing instructions executable bythe processor such that the computer is programmed to: identify acurrent state of a vehicle; plot a maximum brake torque that can beapplied in the vehicle over a period of time based on data continuallyreceived from at least one of a vehicle component and a vehicle system;determine a desired acceleration profile to follow based at least inpart on the maximum brake torque plot; and control an acceleration ofthe vehicle based at least in part on the desired acceleration profile.2. The system of claim 1, wherein the current state of the vehicleincludes at least one of an internal vehicle state and an environmentalcondition.
 3. The system of claim 1, wherein the computer is furtherprogrammed to determine the current state of the vehicle from at least acomponentry status, a controller area network (CAN) bus status, a powersupply level, a current vehicle speed and a tire saturation.
 4. Thesystem of claim 1, wherein the maximum brake torque plot is determinedfrom at least one of a brake pad status, a hydraulic pressure status, asize of the vehicle, a mass of the vehicle, a vehicle payload, a towedobject mass, a road grade value, a road surface mu, a split friction mu,a brake pad mu, a pitch angle of the vehicle, a load distribution and ahydraulic brake pressure distribution.
 5. The system of claim 1, whereinthe computer is further programmed to detect a brake system fault. 6.The system of claim 5, wherein the brake system fault is at least one ofa brake hydraulic circuit failure, a worn brake pad, and a deviation ofbrake pad friction.
 7. The system of claim 1, wherein the computer isfurther programmed to determine the desired acceleration profile tofollow from at least one of a map stored in the memory, a desired routeto follow, a communication from a second vehicle, a communication froman external road infrastructure system, and an obstacle detectionsensor.
 8. The system of claim 7, wherein the obstacle detection sensorincludes at least one of a LIDAR sensor, a SONAR sensor and an opticalrange determination system.
 9. A method, comprising: identifying acurrent state of a vehicle; plotting a maximum brake torque that can beapplied in the vehicle over a period of time based on data continuallyreceived from at least one of a vehicle component and a vehicle system;determining a desired acceleration profile to follow based at least inpart on the maximum brake torque plot; and controlling an accelerationof the vehicle based at least in part on the desired accelerationprofile.
 10. The method of claim 9, wherein the current state of thevehicle includes at least one of an internal vehicle state and anenvironmental condition.
 11. The method of claim 9, further comprisingdetermining the current state of the vehicle from at least a componentrystatus, a controller area network (CAN) bus status, a power supplylevel, a current vehicle speed and a tire saturation.
 12. The method ofclaim 9, wherein the maximum brake torque plot is determined from atleast one of a brake pad status, a hydraulic pressure status, a size ofthe vehicle, a mass of the vehicle, a vehicle payload, a towed objectmass, a road grade value, a road surface mu, a split friction mu, abrake pad mu, a pitch angle of the vehicle, a load distribution and ahydraulic brake pressure distribution.
 13. The method of claim 9,further comprising detecting a brake system fault.
 14. The method ofclaim 13, wherein the brake system fault is at least one of a brakehydraulic circuit failure, a worn brake pad, and a deviation of brakepad friction.
 15. The method of claim 9, further comprising determiningthe desired acceleration profile to follow from at least one of a mapstored in the memory, a desired route to follow, a communication from asecond vehicle, a communication from an external road infrastructuresystem, and an obstacle detection sensor.
 16. The method of claim 15,wherein the obstacle detection sensor includes at least one of a LIDARsensor, a SONAR sensor and an optical range determination system.